I do suggest you learn Perl. (It would not hurt to forget PHP, too :P.)

I must warn you that writing CGI programs will be a little less convenient than PHP, but it will pay off in the long run (the larger the project, the larger the pay off). I find writing a small website in PHP easier than Perl (PHP was built for that stuff, right?).

Regarding module usage: installing them can occasionally be painful (see: PerlMagick) but for the most part it is an easy one-liner in your terminal. Updating is the same.

And, to top it off, I present my favorite reason for learning Perl: Perl in Latin.